The present invention relates to a recording method and an optical disk device, wherein a record mark different in physical properties from the other portion is formed on a record medium to record information, and particularly to a recording method for a DVD-RAM medium using a phase change optical recording material, and an optical disk device using it.
As rewritable type DVD-RAM using a phase change optical material, those of 2× speed, 3× speed, and 5× speed have been standardized, and a super multi drive coping with those have been already produced. At the present in which spread of recording type DVD drives has advanced, an increase in recording/reproducing speed is the most important technical development issue. The present writer and others realized 16× speed recording using DVD-RAM first in the world, and published an outline of the technique as a news release (Outline of drive technique: http://www.hitachi.co.jp/New/cnews/month/2004/04/0422a. html, Outline of medium technique: http://www.maxell.co.jp/company/news/2004/040422.html).
Further, in an optical disk device capable of recording on a DVD-RAM medium, for guaranteeing the reliability of recorded data, conditions of recording power and pulse are calibrated by trial writing. As an example of a conventional trial writing technique, JP-A-10-320777 discloses a technique in which, not a jitter value is directly measured, but a logical pulse called error pulse is generated when the phase difference between a data edge and a clock edge has become a predetermined value or more; the jitter value is equivalently evaluated by counting the number of error pulses; and using it, the recording power is made appropriate.
Further, WO01/011614 discloses a trial writing technique for 4.7 GB DVD-RAM using a table reference type adaptive recording strategy in accordance with a space length and a mark length after and behind. Therein, sort processing is performed with making an error pulse correspond to a table of the recording strategy, and pulse conditions of recording laser light are made appropriate in order that the error pulse value of each item in the table becomes the minimum. Although actual sort processing requires two of 4×4 tables, because a logical pulse called error pulse is used for signal evaluation, there is a merit that sort processing can easily be realized by logical LSI.
For put a drive device and a medium in practical use using the above techniques, there are the following two problems:
(Problem 1) Guarantee of compatibility of recording parameters and realization of CAV (Constant Angular Velocity) recording.
(Problem 2) Improvement of S/N ratio upon high-speed reproduction and guarantee of storage life of data.
First, the problem 1 will be described. For making 16× speed recording on DVD-RAM, because the linear velocity reaches about 66 m/s, the rotational speed of the medium reaches about 11,000 rpm even in the outermost peripheral zone. In general, in case of a DVD disk using a plastic base, the natural vibration of the medium increases as the rotational speed increases, and not only the noise increases, but also the medium is broken in the worst case. Thus, the upper limit of the rotational speed of the medium is about 15,000 rpm at the maximum. Because the rotational speed of the medium exceeds 25,000 rpm for obtaining the linear velocity of 16× speed on the innermost circumference, it can not be realized at present. Therefore, for realizing high-speed recording on DVD-RAM, it is required to record by CAV method in which the rotational speed of the medium is substantially constant. At this time, the linear velocity changes in proportion to the radial position, and it is about 6× speed on the innermost circumference and about 16× speed on the outermost circumference. In the format of DVD-RAM, for studying conditions of recording power and pulse, there are trial writing areas in the innermost circumferential zone and the outermost circumferential zone. Thus, recording conditions for the other zone must be set from the recording conditions of the innermost circumferential zone and the outermost circumferential zone.
Next, the problem 2 will be described. Not limiting to the case of DVD-RAM, for realizing recording at a high speed, because the power necessary for recording becomes large, a higher-power semiconductor laser must be installed in the drive device. In general, the laser noise increases as the power of the semiconductor laser increases. Further, if the reproduction speed is increased, influence by amplifier noise and laser noise contained in a reproduction signal increases to correspond to the spread of band. Therefore, for reproducing record information at a high speed with high reliability, some S/N ratio improving means is required.